Method and apparatus for estimating motion vector using plurality of motion vector predictors, encoder, decoder, and decoding method

ABSTRACT

Provided are a method and apparatus for estimating a motion vector using a plurality of motion vector predictors, an encoder, a decoder, and a decoding method. The method includes calculating spatial similarities between the current block and the plurality of neighboring partitions around the current block, selecting at least one of the neighboring partitions based on the calculated spatial similarities, and estimating a motion vector of the selected partition as the motion vector of the current block.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation of U.S. application Ser. No.11/964,844 filed Dec. 27, 2007, which claims priority from Korean PatentApplication No. 10-2007-0000710 filed on Jan. 3, 2007 and Korean PatentApplication No. 10-2007-0044226 filed on May 7, 2007, the disclosures ofwhich are incorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods and apparatuses consistent with the present invention generallyrelate to video coding and decoding, and more particularly, toestimating a motion vector using a plurality of motion vectorpredictors.

2. Description of the Related Art

Inter-frame and intra-frame predictions are widely used video encodingtechniques. Intra-frame prediction uses a high correlation between graylevels of adjacent pixels in a single frame. Inter-frame prediction usessimilarities between consecutive frames in a video sequence. As long asa sharp change does not occur in a moving picture, many parts of themoving picture change little between consecutive frames. In particular,motion-vector estimation is one of a variety of video encodingtechniques used in inter-frame prediction. Motion-vector estimation isdesigned to process an image by differentially encoding motion vectorsobtained by motion estimation. Generally, a motion vector of a block hasa close correlation with a motion vector of a neighboring partition. Forthis reason, the amount of bits to be encoded can be reduced bypredicting a motion vector of a current block from the motion vector ofa neighboring partition and encoding only a differential vector betweenthese two motion vectors.

FIGS. 1A and 1B illustrate neighboring partitions used for related artmotion estimation.

Referring to FIG. 1A, a current macroblock E and its neighboringpartitions A, B, and C are the same in shape, and predictive encoding ofa motion vector uses the median value of horizontal components andvertical components of motion vectors of a block A located to the leftof the current macroblock E, a block B located above the current blockE, and a block C located above and to the right of the current block E.

In FIG. 1B, the current macroblock E and its neighboring partitions A,B, and C are different in shape, and the motion vector of the currentmacroblock E is estimated as follows.

(1) If a neighboring partition located to the left of the currentmacroblock E is divided into several blocks, a block A located uppermostamong those blocks is used for motion estimation. If a neighboringpartition located above the current macroblock E is divided into severalblocks, a block B located leftmost among those blocks is used for motionestimation. The median value of horizontal components and verticalcomponents of motion vectors of the block A, the block B, and a block Clocated above and to the right of the current macroblock E is used forpredictive encoding of the motion vector of the current macroblock E.

(2) However, if the current macroblock E to be encoded is not a regularsquare in shape, i.e., the current macroblock E is composed of 16×8 or8×16 pixels, the motion vector of the current macroblock E is estimatedbased on the size of a motion compensation block without using themedian value, as follows.

(i) If the current macroblock E is composed of 16×8 pixels, the block Blocated above the current block E and the block A located to the left ofthe current macroblock E are used for motion estimation.

(ii) If the current macroblock E is composed of 8×16 pixels, the block Alocated to the left of the current macroblock E and the block C locatedabove and to the right of the current block E are used for motionestimation.

(3) In a skip macroblock mode, estimation is performed as described in(1).

As described above, at least one neighboring block may be used forestimation of a motion vector of the current block. However, accordingto the prior art, only typical neighboring blocks are available and, outof those neighboring blocks, a block that is similar to the currentblock, i.e., the block having the same motion as the current block, isuseful, but the other blocks are not. Therefore, there is a need to usea plurality of other neighboring blocks for accurate estimation as wellas those typical neighboring blocks. In this case, processing ofinformation about neighboring blocks used for motion estimation is alsorequired.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for estimating amotion vector, in which useful neighboring partitions are estimated soas to estimate a motion vector of a current block and information aboutestimated neighboring partitions is processed.

According to one aspect of the present invention, there is provided amethod of estimating a motion vector of a current block. The methodincludes calculating spatial similarities between the current block anda plurality of neighboring partitions around the current block,selecting at least one of the neighboring partitions based on thecalculated spatial similarities, and estimating a motion vector of theselected partition as the motion vector of the current block.

During the calculation of the spatial similarities, an average value ofpixels of the current block and an average value of pixels of each ofthe neighboring partitions may be used and the average value of thepixels of the current block may be calculated using pixels that touchthe current block from among the pixels of the neighboring partitions.

During the calculation of the spatial similarities, the spatialsimilarities may be allocated to the neighboring partitions according toa spatial order previously agreed between an encoder and a decoder.

The method may further include transmitting motion information betweenthe motion vector of the current block and the estimated motion vectorof the current block and partition information for reconstruction of themotion vector of the current block.

In the estimating, when a plurality of neighboring partitions areselected, a motion vector of one of the selected neighboring partitionsmay be estimated as the motion vector of the current block.

In the estimating, when a plurality of neighboring partitions areselected, the median value of motion vectors of the selected neighboringpartitions may be estimated as the motion vector of the current block.

In the estimating, when a plurality of neighboring partitions areselected, a sum of weighted motion vectors of the selected neighboringpartitions may be estimated as the motion vector of the current block.

In the estimating, a motion vector of a partition in a reference frame,which is located in the spatially same position as the current block,may be estimated as the motion vector of the current block.

According to another aspect of the present invention, there is provideda method of estimating a motion vector of a current block. The methodincludes searching at least one reference frame using motion vectors ofa plurality of neighboring partitions around the current block in orderto search for blocks corresponding to the current block, calculatingsimilarities between neighboring pixels that are adjacent to each of thefound blocks and neighboring pixels that are adjacent to the currentblock, and estimating one of the motion vectors of the partitions as themotion vector of the current block based on the calculation result.

According to another aspect of the present invention, there is provideda computer-readable recording medium having recorded thereon a programfor executing the method.

According to another aspect of the present invention, there is providedan apparatus for estimating a motion vector of a current block usingmotion vectors of a plurality of neighboring partitions around thecurrent block. The apparatus includes a spatial similarity calculationunit calculating spatial similarities between the current block and theplurality of neighboring partitions around the current block, apartition selection unit selecting at least one of the neighboringpartitions based on the calculated spatial similarities, and a motionvector estimation unit estimating a motion vector of the selectedpartition as the motion vector of the current block.

According to another aspect of the present invention, there is provideda video encoder. The video encoder includes a motion estimation unitgenerating a current block and a motion vector of each of a plurality ofneighboring partitions around the current block, a motion vectorestimation unit calculating spatial similarities between the currentblock and the plurality of neighboring partitions around the currentblock, selecting at least one of the neighboring partitions based on thecalculated spatial similarities, and estimating a motion vector of theselected partition as the motion vector of the current block, and anentropy-coding unit performing entropy-coding on motion informationbetween the motion vector of the current block and the estimated motionvector of the current block and partition information for reconstructionof the motion vector of the current block.

According to another aspect of the present invention, there is provideda video decoder. The video decoder includes an entropy-decoding unitperforming entropy-decoding on a residual block, motion information, andpartition information from an encoded bitstream, a motion vectorestimation unit calculating spatial similarities between a current blockand a plurality of neighboring partitions around the current block,selecting at least one of the neighboring partitions based on thecalculated spatial similarities, estimating a motion vector of theselected partition as the motion vector of the current block, adding thedecoded motion information to the estimated motion vector of the currentblock in order to reconstruct the motion vector of the current block,and a macroblock reconstruction unit reconstructing the current blockfrom the decoded residual block using the reconstructed motion vector.

According to another aspect of the present invention, there is provideda decoding method. The decoding method includes performingentropy-decoding on a residual block, motion information, and partitioninformation from an encoded bitstream, calculating spatial similaritiesbetween a current block and a plurality of neighboring partitions aroundthe current block, selecting at least one of the neighboring partitionsbased on the calculated spatial similarities, estimating a motion vectorof the selected partition as the motion vector of the current block,adding the decoded motion information to the estimated motion vector ofthe current block in order to reconstruct the motion vector of thecurrent block, and reconstructing the current block from the decodedresidual block using the reconstructed motion vector.

According to another aspect of the present invention, there is provideda computer-readable recording medium having recorded thereon a programfor executing the decoding method.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail an exemplary embodiment thereof withreference to the attached drawings in which:

FIGS. 1A and 1B illustrate neighboring partitions used for conventionalmotion estimation;

FIG. 2 illustrates neighboring partitions used for motion estimationaccording to an exemplary embodiment of the present invention;

FIG. 3A is a flowchart of a method of estimating a motion vector of acurrent block according to an exemplary embodiment of the presentinvention;

FIG. 3B is a flowchart of a method of estimating a motion vector of acurrent block according to another exemplary embodiment of the presentinvention;

FIG. 4A is a view for explaining calculation of spatial similaritiesbetween the current block and its neighboring partitions according to anexemplary embodiment of the present invention;

FIGS. 4B and 4C are views for explaining calculation of spatialsimilarities between neighboring pixels that are adjacent to the currentblock and neighboring pixels that are adjacent to each reference blockthat corresponds to the current block according to an exemplaryembodiment of the present invention;

FIG. 5A is a block diagram of an apparatus for estimating a motionvector according to an exemplary embodiment of the present invention;

FIG. 5B is a block diagram of an apparatus for estimating a motionvector according to another exemplary embodiment of the presentinvention;

FIG. 6 is a block diagram of an encoder including the apparatus forestimating a motion vector according to an exemplary embodiment of thepresent invention;

FIG. 7 is a block diagram of a decoder according to an exemplaryembodiment of the present invention; and

FIG. 8 is a flowchart of a decoding method according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Hereinafter, an exemplary embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings. Itshould be noted that like reference numerals refer to like elementsillustrated in one or more of the drawings. It would be obvious to thoseof ordinary skill in the art that many specifics like elements of acircuit are provided only to facilitate understanding of the presentinvention and the present invention can be implemented without thosespecifics. In the following description of the present invention, adetailed description of known functions and configurations incorporatedherein will be omitted for conciseness and clarity.

FIG. 2 illustrates neighboring partitions used for motion estimationaccording to an exemplary embodiment of the present invention. Referringto FIG. 2, a motion vector of a current block E can be estimated usingnot only neighboring partitions A, B, and C according to the related artbut also by using other neighboring partitions A1, A2, B1, and B2. Thecurrent block E may be a 16×16 macroblock and the size of a neighboringpartition may be smaller than the current block E and may be one of16×8, 8×16, 8×4, 4×8, and 4×4.

FIG. 3A is a flowchart of a method of estimating a motion vector of acurrent block according to an exemplary embodiment of the presentinvention, and FIG. 4A is a view for explaining calculation of spatialsimilarities between the current block and its neighboring partitionsaccording to an exemplary embodiment of the present invention.

Referring to FIG. 3A, an average value of pixels of the current block Eand an average value of pixels of each of the neighboring partitions A,B, A1, A2, B1, B2, and C are calculated in operation S300, in order toselect neighboring partitions having spatial similarity with the currentblock E.

In operation S301, the similar neighboring partitions are selected aspredictors of the current block using the calculated averages. Thepredictors are blocks that are to be compared with the current block forobtaining a motion vector difference (MVD).

More specifically, when the average value of pixels of the current blockis a first average and the average value of pixels of a neighboringpartition is a second average, the neighboring partition is selected asa predictor of the current block if the absolute value of a differencebetween the first average and the second average is less than apredetermined threshold.

In particular, the average value of pixels of the current block and theaverage value of pixels of each of a plurality of neighboring partitionsaround the current block may be used for calculation of a spatialsimilarity and the average value of pixels of the current block may becalculated using pixels that touch the current block from among thepixels of the neighboring partitions. During calculation of a spatialsimilarity, the spatial similarity is allocated to each of theneighboring partitions according to a spatial order agreed previouslybetween an encoder and a decoder.

In operation S302, a motion vector of the selected neighboring partitionis estimated as the motion vector of the current block. At least twoneighboring partitions may have been selected in operation S301, as willbe described with reference to FIG. 4.

FIG. 4A is a view for explaining calculation of spatial similaritiesbetween the current block and its neighboring partitions according to anexemplary embodiment of the present invention. In FIG. 4A, it is assumedthat the current block E is a 16×16 macroblock, a neighboring partitionA is composed of 8×4 pixels, a neighboring partition A1 is composed of8×4 pixels, a neighboring partition A2 is composed of 8×8 pixels, aneighboring partition B is composed of 4×8 pixels, a neighboringpartition B1 is composed of 4×8 pixels, a neighboring partition B2 iscomposed of 8×8 pixels, and a neighboring partition C is composed of16×8 pixels. In addition, it is assumed that an absolute value of adifference between an average value of pixels of the current block E andan average value of pixels of each of the neighboring partitions A2, B1,and B2 is less than a predetermined threshold.

According to an exemplary embodiment of the present invention, a motionvector of the current block E can be estimated as follows in (i), (ii),(iii) or (iv).

(i) One of the neighboring partitions A2, B1, and B2 is selected and amotion vector of the selected neighboring partition is estimated as themotion vector of the current block E,

(ii) A combination of the neighboring partitions A2, B1, and B2, e.g., acombination formula ₃C₂, is selected and the median value of xcomponents and y components of motion vectors of the selectedneighboring partitions is estimated as the motion vector of the currentblock E.

(iii) If motion vectors of the neighboring partitions A2, B1, and B2 areMVPA2, MVPB1, and MVPB2, a sum of weighted motion vectors, e.g.,a*MVPA2+β*MVPB1+γ*MVPB2, is estimated as the motion vector of thecurrent block E.

Information about neighboring partitions, i.e., partition information,complies with a rule previously reserved for a decoder. For example, thepartition information may indicate that a motion vector of a neighboringpartition located to the left of the current block from amongneighboring partitions having spatial similarities with the currentblock is estimated as the motion vector of the current block or themedian value of motion vectors of the neighboring partitions isestimated as the motion vector of the current block. When weights areused, weight coefficients (α, β, γ) have to be transmitted to a decoderas a partition type.

(iv) A motion vector of a partition in a reference frame, which islocated in a position that spatially corresponds to that of the currentblock, may be estimated as the motion vector of the current block. Apartition in a temporally close reference frame, which is located in aposition that spatially corresponds to that of the current block, i.e.,the partition in the reference frame, which is located in the spatiallysame position as the current block, is highly likely to have a motionthat is similar to that of the current block. Thus, the motion vector ofthe partition, which is located in the spatially same position as thecurrent block, may be estimated as the motion vector of the currentblock.

Information about neighboring partitions, i.e., partition information,complies with a rule previously reserved for a decoder. For example, thepartition information may indicate that a motion vector of a neighboringpartition located to the left of the current block from amongneighboring partitions having spatial similarities with the currentblock is estimated as the motion vector of the current block or themedian value of motion vectors of the neighboring partitions isestimated as the motion vector of the current block. When weights areused, weight coefficients (α, β, γ) have to be transmitted to a decoderas a partition type.

FIG. 3B is a flowchart of a method of estimating a motion vector of acurrent block according to another exemplary embodiment of the presentinvention, and FIGS. 4B and 4C are views for explaining calculation ofspatial similarities between pixels that are adjacent to the currentblock and pixels that are adjacent to each block that corresponds to thecurrent block according to an exemplary embodiment of the presentinvention. Referring to FIG. 3B, in operation 310, at least onereference frame is searched using motion vectors of the plurality ofneighboring partitions A, B, C, A1, A2, B1, B2, and C that are adjacentto a current block 410 in order to search for blocks 420 through 422that correspond to the current block 410. It is assumed that the currentblock 410 is the same as the current block E illustrated in FIG. 3A.

The motion vectors of the neighboring partitions A, B, C, A1, A2, B1,B2, and C are estimated as the motion vector of the current block 410.For example, the motion vector of the partition A illustrated in FIG. 3Amay be an estimated motion vector MVP1, the motion vector of thepartition B illustrated in FIG. 3A may be an estimated motion vectorMVP2, and the motion vector of the partition C illustrated in FIG. 3Amay be an estimated motion vector MVP3.

In operation 311, similarities between neighboring pixels 423 through425 that are adjacent to the found blocks 420 through 422 correspondingto the current block 410 and neighboring pixels 411 that are adjacent tothe current block 410 are calculated.

Preferably, but not necessarily, the similarities may be calculated bycalculating sums of absolute differences (SADs) between the pixels 423through 425 and the pixels 411.

For SAD calculation in operation 311, it is not necessary to use all theneighboring pixels 423 through 425 that are adjacent to the blocks 420through 422 corresponding to the current block 410 and the neighboringpixels 411 that are adjacent to the current block 410. As illustrated inFIG. 4C, the similarities may be calculated by calculating SADs betweenonly some of the neighboring pixels 423 through 425 and the neighboringpixels 411. In FIG. 4C, among the neighboring pixels 423 through 425 andthe neighboring pixels 411, only neighboring pixels that are located tothe left of and above, to the right of and above, and to the left of andbelow a corresponding block are used to calculate the similarities.

In operation 312, one of the motion vectors of the neighboringpartitions A, B, C, A1, A2, B1, B2, and C is estimated as the motionvector of the current block based on the similarities calculated inoperation 311.

If SADs have been calculated for the similarities in operation 311, amotion vector used to search for a block that is adjacent to pixelshaving the smallest SAD is estimated as the motion vector of the currentblock. For example, if an SAD between the neighboring pixels 411 of thecurrent block 410 and the neighboring pixels 423 of the block 420 foundusing the motion vector MVP1 is smallest among the calculated SADs andthus a similarity between the neighboring pixels 411 and the neighboringpixels 423 is highest, the motion vector used to search for the block410, i.e., the motion vector MVP1, is estimated as the motion vector ofthe current block.

However, it is not necessary to estimate a motion vector used to searchfor a block that is adjacent to pixels having the smallest SAD as themotion vector of the current block. In spite of corresponding to thesmallest SAD, the motion vector may not be an appropriately estimatedmotion vector when considering the overall rate-distortion (R-D) cost ofthe current block. Therefore, N motion vector candidates, i.e., aplurality of motion vector candidates corresponding to smaller SADs, areselected and a motion vector guaranteeing low R-D cost among theselected motion vector candidates is estimated as the motion vector ofthe current block.

In this case, information indicating which motion vector has among theplurality of motion vector candidates been estimated as the motionvector of the current block has to be transmitted to a decoder.

It is assumed that motion vectors MVP1 and MVP2 among motion vectorsMVP1, MPV2, and MVP3 illustrated in FIG. 4B correspond to small SADs andan SAD corresponding to the motion vector MVP1 is smaller than an SADcorresponding to the motion vector MVP2. The two motion vectors MVP1 andMVP2 are estimated as the motion vector of the current block andencoding is performed using the estimated motion vector. As a result ofencoding, if it is determined that an R-D cost corresponding to a casewhere the motion vector MVP2 is estimated as the motion vector of thecurrent block is lower than that corresponding to the other case, themotion vector MVP2 is estimated as the motion vector of the currentblock.

As discussed above with reference to FIGS. 3B, 4B, and 4C, it is notnecessary to use the pixels 411 and the pixels 423 through 425 that areimmediately adjacent to the borders of the block 410 and the blocks 420through 422 for similarity calculation. Pixels spaced by a predetermineddistance from the borders of the block 410 and the blocks 420 through422 may also be used as long as they have correlations with the block410 and the blocks 420 through 422.

However, those of ordinary skill in the art may understand that themethods described above are only examples and various combinations areavailable.

FIG. 5A is a block diagram of an apparatus 500 for estimating a motionvector according to an exemplary embodiment of the present invention.Referring to FIG. 5A, the apparatus 500 includes a spatial similaritycalculation unit 501, a partition selection unit 502, and a motionvector estimation unit 503.

The spatial similarity calculation unit 501 calculates an average valueof pixels of the current block E and an average value of pixels of eachof the neighboring partitions A, B, A1, A2, B1, B2, and C around thecurrent block E. The calculated averages are transmitted to thepartition selection unit 502.

If the average value of the pixels of the current block E is a firstaverage and the average value of the pixels of each of the neighboringpartitions A, B, A1, A2, B1, B2, and C is a second average, thepartition selection unit 502 selects a neighboring partition (orneighboring partitions) as a predictor of the current block E when anabsolute value of a difference between the first average and the secondaverage corresponding to the neighboring partition is less than apredetermined threshold. Information about the selected neighboringpartition(s) is transmitted to the motion vector estimation unit 503.

The motion vector estimation unit 503 estimates the motion vector of thecurrent block E using a motion vector (or motion vectors) of theselected neighboring partition(s) as described above with reference toFIGS. 3A and 4A. At least two neighboring partitions may be selected andmotion estimation in this case may be performed as described above withreference to FIGS. 3A and 4A.

FIG. 5B is a block diagram of the apparatus 500 for estimating a motionvector according to another exemplary embodiment of the presentinvention. Referring to FIG. 5B, the apparatus 500 includes a searchunit 511, a similarity calculation unit 512, and a motion vectorestimation unit 513.

The search unit 511 searches at least one reference frame using themotion vectors of the plurality of neighboring partitions A, B, C, A1,A2, B1, B2, and C that are adjacent to the current block 410 in order tosearch for the blocks 420 through 422 corresponding to the current block410. As set forth with reference to FIG. 3B, the current block 410 isassumed to be the same as the current block E illustrated in FIG. 3A.

The similarity calculation unit 512 calculates similarities between theneighboring pixels 423 through 425 that are adjacent to the found blocks420 through 422, respectively, and the neighboring pixels 411 that areadjacent to the current block 410.

For similarity calculation, the similarity calculation unit 512calculates SADs between the neighboring pixels 423 through 425 and theneighboring pixels 411.

The motion vector estimation unit 513 estimates the motion vector of thecurrent block 410 based on the calculation result obtained by thesimilarity calculation unit 512. Detailed methods for motion vectorestimation have already been described with reference to FIGS. 3B, 4B,and 4C.

FIG. 6 is a block diagram of an encoder 600 including the apparatus 500according to an exemplary embodiment of the present invention.

Referring to FIG. 6, an addition unit 601 calculates a differencebetween image data of a current frame input from the outside andmotion-compensated video data received from a motion compensation unit609 and transmits the difference to a frequency conversion unit 602. Ifa current macroblock is subject to inter-mode coding, the addition unit601 outputs the difference between the image data input from the outsideand the motion-compensated image data to the frequency conversion unit602.

The frequency conversion unit 602 performs discrete cosinetransformation (DCT) on image data received from the addition unit 601in order to convert spatial-domain values into frequency-domain valuesand outputs the conversion frequency-domain values to a quantizationunit 603.

The quantization unit 603 quantizes the frequency-domain values receivedfrom the frequency conversion unit 602 and outputs the quantizedfrequency-domain values to an entropy-coding unit 604.

The entropy-coding unit 604 performs entropy-coding on the quantizedfrequency-domain values received from the quantization unit 603, onmotion information, and on partition information received from theapparatus 500 in order to generate an encoded bitstream.

An inverse quantization unit 605, an inverse frequency conversion unit606, a frame storing unit 607, a motion estimation unit 608, the motioncompensation unit 609, and the apparatus 500 constitute a set ofmodules/devices for motion compensation.

The inverse quantization unit 605 performs inverse quantization on thequantized frequency-domain values received from the quantization unit603 and outputs the inversely quantized frequency-domain values to theinverse frequency conversion unit 606.

The inverse frequency conversion unit 606 converts the inverselyquantized frequency-domain values received from the inverse quantizationunit 605 into spatial-domain values and outputs the spatial-domainvalues to an addition unit 606 a.

The addition unit 606 a adds image data output from the inversefrequency conversion unit 606 to image data received from the motioncompensation unit 609 in order to generate reference image data formotion compensation. The generated reference image data is stored in theframe storing unit 607.

The frame storing unit 607 stores image data of a reference framereceived from the addition unit 606 a.

The motion estimation unit 608 performs motion estimation between imagedata of a current frame input from the outside and image data stored inthe frame storing unit 607 in order to calculate motion vectors. Themotion vectors calculated by the motion estimation unit 608 aretransmitted to the motion compensation unit 609 and the apparatus 500.

The motion compensation unit 609 performs motion compensation on imagedata stored in the frame storing unit 607 using the motion vectorscalculated by the motion estimation unit 608 in order to generatemotion-compensated image data. The motion-compensated image data istransmitted to the addition unit 601 and the addition unit 606 a.

The apparatus 500 includes the spatial similarity calculation unit 501,the partition selection unit 502, and the motion vector estimation unit503 as described with reference to FIG. 5A. The spatial similaritycalculation unit 501 calculates an average value of pixels of thecurrent block E and an average value of pixels of each of theneighboring partitions A, B, A1, A2, B1, B2, and C around the currentblock E.

If the average value of pixels of the current block E is a first averageand the average value of pixels of each of the neighboring partitions A,B, A1, A2, B1, B2, and C is a second average, the partition selectionunit 502 selects a neighboring partition (or neighboring partitions) asa predictor of the current block E when an absolute value of adifference between the first average and the second averagecorresponding to the neighboring partition is less than a predeterminedthreshold. Information about the selected neighboring partition(s) istransmitted to the motion vector estimation unit 503.

The motion vector estimation unit 503 estimates the motion vector of thecurrent block E using a motion vector (or motion vectors) of theselected neighboring partition(s). The partition information and motioninformation are output to the entropy-coding unit 604. The motioninformation indicates a difference between the estimated motion vectorof the current block and the motion vector of the selected neighboringpartition.

These methods have already been described in detail with reference toFIGS. 3A and 4A.

According to another exemplary embodiment of the present invention, theapparatus 500 includes the search unit 511, the similarity calculationunit 512, and the motion vector estimation unit 513 as illustrated inFIG. 5B. The search unit 511 searches at least one reference frame(s)using the motion vectors of the plurality of neighboring partitions A,B, C, A1, A2, B1, B2, and C that are adjacent to the current block 410in order to search for the blocks 420 through 422 corresponding to thecurrent block.

The similarity calculation unit 512 calculates similarities between theneighboring pixels 423 through 425 that are adjacent to the found blocks420 through 422, respectively, and the neighboring pixels 411 that areadjacent to the current block 410. For similarity calculation, thesimilarity calculation unit 512 calculates SADs between the neighboringpixels 423 through 425 and the neighboring pixels 411.

The motion vector estimation unit 513 estimates the motion vector of thecurrent block 410 based on the calculation result obtained by thesimilarity calculation unit 512. Partition information and motioninformation are output to the entropy-coding unit 604. The motioninformation indicates a difference between the estimated motion vectorof the current block and the motion vector of the neighboring partitionused to estimate the motion vector of the current block.

Detailed methods for motion vector estimation have already beendescribed with reference to FIGS. 3B, 4B, and 4C.

FIG. 7 is a block diagram of a decoder 700 according to an exemplaryembodiment of the present invention, in which the decoder 700 includesan entropy-decoding unit 701, an inverse quantization unit 702, aninverse frequency conversion unit 703, a frame storing unit 704, amotion compensation unit 705, an addition unit 706, and a motion vectorestimation unit 707.

Referring to FIG. 7, the entropy-decoding unit 701 performsentropy-decoding on an encoded bitstream and transmits theentropy-decoded bitstream to the inverse quantization unit 703 and themotion vector estimation unit 707. In particular, in the case ofinter-mode coding, the entropy-decoding unit 701 extracts motioninformation and partition information associated with the currentmacroblock and entropy-decoded image data and outputs the extractedimage data to the inverse quantization unit 702 and the extracted motioninformation and partition information to the motion vector estimationunit 707.

The inverse quantization unit 702 performs inverse quantization on theentropy-decoded image data output from the entropy-decoding unit 702 andoutputs the inversely quantized image data to the inverse frequencyconversion unit 703.

The inverse frequency conversion unit 703 converts the inverselyquantized image data output from the inverse quantization unit 702 intospatial-domain values and outputs the spatial-domain values to theaddition unit 706.

The addition unit 706 adds the motion-compensated image data receivedfrom the motion compensation unit 705 to the inversely quantized imagedata received from the inverse frequency conversion unit 703 in order togenerate reconstructed image data. The output of the addition unit 706is decoded image data of the current frame.

The frame storing unit 704 stores image data of a frame, which is outputfrom the addition unit 706.

The motion vector estimation unit 707 estimates a motion vector of thecurrent block using the motion information extracted by theentropy-decoding unit 701 and a reference block of the frame storingunit 704. The estimated motion vectors are output to the motioncompensation unit 705.

More specifically, the motion vector estimation unit 707 estimates themotion vector of the current block in the same way as the apparatus 500included in the encoder 600 illustrated in FIG. 6 estimates the motionvector. Thus, the motion vector estimation unit 707 may be configured inthe same manner as the apparatus 500 illustrated in FIG. 6.

The motion compensation unit 705 applies motion vectors and partitioninformation received from the motion vector estimation unit 707 to imagedata of a reference frame stored in the frame storing unit 704 in orderto perform motion compensation. The motion-compensated image data isoutput to the addition unit 706.

FIG. 8 is a flowchart of a decoding method according to an exemplaryembodiment of the present invention.

Referring to FIG. 8, entropy-decoding is performed on motioninformation, partition information, and a residual block from an encodedbitstream in operation S801.

In operation S802, a motion vector of the current block is reconstructedusing the decoded motion information and partition information. Morespecifically, spatial similarities between the current block and aplurality of neighboring partitions around the current block arecalculated based on the decoded partition information. At least one ofthe neighboring partitions is selected based on the calculated spatialsimilarities and a motion vector of the selected neighboring partitionis estimated as the motion vector of the current block. Next, the motioninformation is added to the estimated motion vector in order toreconstruct the motion vector of the current block.

According to another exemplary embodiment of the present invention, atleast one reference frame(s) is searched using motion vectors of aplurality of neighboring partitions around the current block, which aredetermined based on decoded partition information, in order to searchfor blocks corresponding to the current block. Similarities betweenneighboring pixels that are adjacent to the found blocks, respectively,and neighboring pixels that are adjacent to the current block arecalculated. One of the motion vectors of the neighboring partitions isestimated as the motion vector of the current block based on thecalculation result, and decoded motion information is added to theestimated motion vector in order to reconstruct the motion vector of thecurrent block.

In operation S803, the motion vector reconstructed in operation S802 isapplied to the decoded reference block in order to generate amotion-compensated block. In addition, the residual block isentropy-decoded in operation S801 and then undergoes inversequantization and inverse frequency conversion in order to generate aspatial-domain residual block. The motion-compensated block and thespatial-domain residual block are added together in order to generatethe current block.

Since it is apparent that neighboring partitions can also be used forthe decoding method and the decoder in order to estimate the motionvector of the current block in the same manner as in the encoder, adetailed description thereof will be omitted.

As described above, according to the exemplary embodiments of thepresent invention, by estimating useful partitions for estimation of themotion vector of the current block and processing information about theestimated partitions, the amount of information transmitted to thedecoder can be reduced.

The present invention can also be embodied as computer-readable code ona computer-readable recording medium. The computer-readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of computer-readablerecording media include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storagedevices. The computer-readable recording medium can also be distributedover a network of coupled computer systems so that the computer-readablecode is stored and executed in a decentralized fashion.

While the present invention has been particularly shown and describedwith reference to an exemplary embodiment thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A method of estimating a motion vector of acurrent block, the method comprising: selecting at least one partitions,which are compared with the current block for obtaining a motion vectordifference, from among a plurality of neighboring partitions around thecurrent block based on spatial similarities between the current blockand the plurality of neighboring partitions; estimating a motion vectorof the selected partition as the motion vector of the current block andgenerating the motion vector difference; and transmitting information onthe motion vector difference and partition information forreconstruction of the motion vector of the current block.
 2. The methodof claim 1, wherein the spatial similarities are calculated based on anaverage value of pixels of the current block and an average value ofpixels of each of the neighboring partitions.
 3. The method of claim 2,wherein the average value of the pixels of the current block iscalculated by using pixels that are contiguous with the current blockfrom among the pixels of the neighboring partitions.
 4. The method ofclaim 1, wherein the spatial similarities are allocated to theneighboring partitions according to a spatial order previously agreedbetween an encoder and a decoder.
 5. The method of claim 1, wherein inthe estimating, if a plurality of neighboring partitions are selected, amotion vector of one of the selected neighboring partitions is estimatedas the motion vector of the current block.
 6. The method of claim 1,wherein in the estimating, if a plurality of neighboring partitions areselected, a median value of motion vectors of the selected neighboringpartitions is estimated as the motion vector of the current block. 7.The method of claim 1, wherein in the estimating, if a plurality ofneighboring partitions are selected, a sum of weighted motion vectors ofthe selected neighboring partitions is estimated as the motion vector ofthe current block.
 8. The method of claim 1, wherein in the estimating,a motion vector of a partition in a reference frame, which is located ina spatially same position as the current block, is estimated as themotion vector of the current block.